It's not usually possible to open an Unpaid Item Case after a Cancel a Transaction case has been opened and closed, even if the
buyer declines.The system won't allow it.
I'd be guessing but I wonder if it has anything to do with a seller having Unpaid Item Assistant set up.
I have read about it happening before though and it's mentioned in this thread:
http://community.ebay.com.au/t5/Selling/Non-paying-buyer-cancel-transaction-or-open-an-unpaid-item-c...
You could try contacting ebay about it but after the response from customer support shown in #15 of the link I posted, I'm not sure you'll get much help from them !
If you do end up with an unpaid item strike, appeal it and I'm positive it will be removed.
